Radically curable urethane prepolymers and their use in dental materials

ABSTRACT

The invention relates to urethane prepolymers, obtainable by reaction of:  
     (A) 15 to 85 wt.-% of one or more α,ω-terminated poly(meth)acrylate diols,  
     (B) 0 to 30 wt.-% of one or more radically curable, polyhydroxy-functional compounds,  
     (C) 14 to 60 wt.-% of one or more polyisocyanates,  
     (D) 1 to 40 wt.-% of a monofunctional compound, reactive vis-à-vis isocyanate groups, which also contains one or more radically curable groupings.  
     as well as their use.

[0001] The present invention describes di- or higher-functionalradically curable urethane prepolymers and their use in polymerizablecompounds. The invention furthermore describes the use of thepolymerizable compounds in the dental field, for example as fillingmaterials, stump build-up materials, fixing cements, temporary crown andbridge materials, dental materials, modelling materials or for thepreparation of inlays, onlays, facing shells, crowns and bridges.

[0002] Materials suitable for such purposes advantageously display ahigh impact strength, high elasticity with high hardness as well as asmall tendency to swell. These properties are largely determined by themonomers used.

[0003] In the state of the art, above all, ethylenically unsaturatedcompounds such as acrylic acid and/or methacrylic acid esters aredescribed as suitable monomers.

[0004] In the dental industry, essentially7,7,9-trimethyl-4,13-dioxo-3,14-dioxa-5,12-diazahexadecane-1,16-dioxy-dimethacrylate(e.g. Plex 666-1, Röhm) for example is used in particular from the groupof the urethane(meth)acrylates, which with its low molecular weight haslittle elastifying effect and improves the impact strength onlyslightly.

[0005] To improve the elastifying properties and the impact strength, inthe lacquer industry for example, a variety of polyurethane oligomersend-functionalized with (meth)acrylate groups which have polyester,polyether, polybutadiene and/or polycarbonate units are used withradically curable systems. However, these systems have a range ofdisadvantages:

[0006] Thus the ester bonds of the polyester urethane(meth)acrylates andof the polycarbonate urethane(meth)acrylates tend towards hydrolysisupon contact with moisture, whereby in particular the mechanical valuesof formulations prepared therefrom are reduced.

[0007] Polyether-based urethane(meth)acrylates show a clearly lowersusceptibility to hydrolysis. However, these systems, due to theirhydrophilicity, display an increased water absorption and thus anincreased tendency to swell and lower strength, which involves areadiness to discolour. Such systems are therefore not suitable foraesthetically demanding applications.

[0008] A further disadvantage of the polyether urethane(meth)acrylateslies in their lack of resistance to oxidation as a result of thedegradation of the oxidative polyether chain.

[0009] Although the polybutadiene urethane(meth)acrylates show excellentelastic properties, they are readily discoloured by the double bondspresent through short-wave radiation as contained in sunlight.

[0010] In principle, urethane(meth)acrylates can also be prepared fromlow-molecular aliphatic and/or aromatic diols. However, these do notshow elastic and impact strength-modifying properties as good as thoseof the above-named urethane(meth)acrylates which contain soft segmentson polyester, polyether, polybutadiene and/or polycarbonate units.

[0011] There is therefore a substantial demand for monomers which incurable compounds lead to an improvement in impact strength, goodelasticity with high hardness and swell only slightly.

[0012] The object of the present invention is to provide monomers fromwhich compounds can be formulated which display an improved impactstrength with simultaneous high hardness and good elasticity.

[0013] Surprisingly, it was found that these requirements are met withurethane prepolymers which can be obtained by reaction of:

[0014] (A) 15 to 85 wt.-%, preferably 20 to 80 wt.-% of one or moreα,ω-terminated poly(meth)acrylate diols,

[0015] (B) 0 to 30 wt.-%, preferably 0 to 20 wt.-% of one or moreradically curable, polyhydroxy-functional compounds,

[0016] (C) 14 to 60 wt.-%, preferably 18 to 50 wt.-% of one or morepolyisocyanates,

[0017] (D) 1 to 40 wt.-%, preferably 2 to 35 wt.-% of a monofunctionalcompound reactive vis-à-vis isocyanate groups, which also contains oneor more radically curable groupings.

[0018] Surprisingly, compounds which were formulated with the monomersaccording to the invention show an extremely small degree of swelling.

[0019] Furthermore, the monomers are toxicologically acceptable and aretherefore suitable in particular for use in the dental field.

[0020] The α,ω-terminated poly(meth)acrylate diols of the component (A)are compounds which contain two terminal hydroxyl groups. Suitablestarting compounds for building up these α,ω-terminatedpoly(meth)acrylate diols and the preparation process for these compoundsare described in detail in EP-B1-0 622 378 and EP-B1-0 205 846. They arecommercially available from Tego under the name “Tego-Diol”.

[0021] The component (B) is radically curable compounds, for example(meth)acrylate-based, which in accordance with DIN 53 240 display OHnumbers preferably from 40 to 700 mg KOH/g and particularly preferablyfrom 80 to 500 mg KOH/g.

[0022] Suitable representatives are for examplepolyhydroxy-group-containing polyester(meth)acrylate prepolymers asdescribed in U.S. Pat. No. 4,206,205, DE-OS40 40 290, DE-OS-33 16 592,DE-OS-37 04 098 and in “UV & EB Curing Formulations for Printing InksCoatings and Paints”, ed. R. Holman and P. Oldring, published by SITATechnology, London (England) 1988, p 36 ff.

[0023] Alternatively, polyhydroxy-group-containingpolyepoxy(meth)acrylate prepolymers which are accessible by reaction ofpolyepoxides with (meth)acrylic acid, and/orpolyhydroxy-group-containing polyurethane(meth)acrylate prepolymers canalso be used.

[0024] Particularly preferred representatives arepolyhydroxy-group-containing polyepoxy(meth)acrylate prepolymers, suchas 2,2-bis[p-(2′-hydroxy-3′-methacryloyloxypropoxy)-phenyl]-propane(bis-GMA) or2,2-bis-[p-(2′hydroxy-3′-acryloyloxypropoxy)-phenyl]-propane (bis-GA)and polyhydroxy-group-containing (meth)acrylate esters such as glycerolmono(meth)acrylate, trimethylolpropane mono(meth)acrylate orpentaerythritol di(meth)acrylate.

[0025] Suitable polyisocyanates of the component (C) are of analiphatic, cycloaliphatic and/or aromatic nature and contain at leasttwo free isocyanate groups. Preferably, diisocyanates X(NCO)₂ are used,X representing an aliphatic hydrocarbon radical with 2 to 12 C atoms, acycloaliphatic hydrocarbon radical with 5 to 18 C atoms, an aromatichydrocarbon radical with 6 to 16 C atoms and/or an araliphatichydrocarbon radical with 7 to 15 C atoms.

[0026] Examples of such diisocyanates are: 1,4-tetramethylenediisocycanate, 1,6-hexamethylene diisocycanate (HDI),2,4,4-trimethyl-hexamethylene diisocycanate, isophorone diisocycanate,4,4′-dicyclohexylmethane diisocycanate, meta- and para-tetramethylxylenediisocycanate, 1,4-phenylene diisocycanate, 2,6- and 2,4-toluenediisocycanate, 1,5-naphthylene diisocycanate, 2,4′ and4,4′-diphenylmethane diisocycanate.

[0027] It is naturally also possible to use, or also use a proportionof, the higher-functional polyisocyanates known from polyurethanechemistry or else modified polyisocyanates, for example containingcarbodiimide groups, allophanate groups, isocyanurate groups and/orbiuret groups. Particularly preferred isocyanates are isophoronediisocyanate and 2,4,4-trimethyl-hexamethylene diisocyanate.

[0028] Compounds of the component (D) contain a functional group whichis reactive vis-à-vis isocyanates, for example a hydroxy group or aminogroup, and also have one or more radically curable groupings. Theradically curable groupings are preferably (meth)acrylate-based. Therepresentatives of this component (D) can also be used as a mixture.

[0029] Suitable representatives are for example 2-hydroxy(meth)acrylate,2-hydroxypropyl (meth)acrylate, glycerol di(meth)acrylate and/ortrimethylolpropane di(meth)acrylate. Particularly preferred are2-hydroxyethyl methacrylate (HEMA) and/or 2-hydroxyethyl acrylate (HEA).

[0030] For the preparation of the urethane prepolymers according to theinvention, for example the components (A) to (C) are introduced firstinto a reactor or fed individually in metered quantities and convertedto an NCO-containing prepolymer under anhydrous conditions, for examplein a temperature range from −20° C. to 160° C., preferably in atemperature range from 0° C. to 130° C. and particularly preferably atemperature range from 20° C. to 100° C.

[0031] The equivalence ratio of isocyanate groups to compounds reactivevis-à-vis isocyanate groups is 1.1:1 to 8:1, preferably 1.5:1 to 4:1.

[0032] The isocyanate polyaddition reaction can take place in thepresence of catalysts known from polyurethane chemistry, for exampleorganotin compounds such as dibutyltin dilaurate or amine catalysts suchas diazabicyclo[2.2.2]octane. Furthermore, the synthesis can take placeboth in the melt and in a suitable solvent which can be added before orduring the prepolymer preparation. Suitable solvents are for exampleacetone, 2-butanone, tetrahydrofurane, dioxane, dimethylformamide,N-methyl-2-pyrrolidone (NMP), ethyl acetate, alkyl ethers of ethyleneand propylene glycol and aromatic hydrocarbons. The use of ethyl acetateas solvent is particularly preferred.

[0033] Measured doses of the component (D) are added complete orportionwise to the NCO-containing prepolymers accompanied by stirringand reacted for example in a temperature range from −20° C. to 160° C.,preferably in a temperature range from 0° C. to 130° C. and particularlypreferably a temperature range from 20° C. to 100° C. The quantity ofcomponent (D) to be used depends on the still present unreactedisocyanate groups of the prepolymer. The measurement of the isocyanatecontent of the prepolymer takes place for example according to DIN 53185.

[0034] For example, the average by weight of the molecular weight(M_(W)) obtained from GPC measurements against polystyrene standards canlie between 400 and 200,000 g/mol, preferably between 500 and 100,000g/mol and particularly preferably between 600 and 50,000 g/mol.Naturally, the molecular weights can also lie outside these rangesprovided it allows the use of the polyurethane prepolymers according tothe invention.

[0035] The urethane prepolymers according to the invention are suitablefor example for the preparation of curable compounds such as dentalcompounds or for coating, pouring and gluing of substrates.

[0036] Curable formulations, for example for use in the dental field,preferably contain the following components:

[0037] (C1) 1 to 70 wt.-%, in particular 2 to 50 wt.-% of urethaneprepolymer according to the invention,

[0038] (C2) 8.9 to 70 wt.-%, in particular 10 to 60 wt.-% of one or moreradically polymerizable monomers,

[0039] (C3) 10 to 90 wt.-%, in particular 10 to 87.9 wt.-% fillers,

[0040] (C4) 0.1 to 5 wt.-%, in particular 0.1 to 3 wt.-% initiators andoptionally activators,

[0041] (C5) 0 to 30 wt.-%, in particular 0 to 20 wt.-% additives,optionally pigments, thixotropic auxiliaries, plasticizers.

[0042] The compounds formulated with the urethane prepolymers accordingto the invention are characterized by particularly good impact strength,good elasticity with high hardness and a surprisingly small tendency toswell.

[0043] As component (C2) are used mono-, di- or higher-functionalethylenically unsaturated compounds, preferably acrylate- and/ormethacrylate-based. These can contain both monomeric andhigher-molecular oligomeric or polymeric acrylates. Furthermore, theycan be used alone or in mixture in the formulations.

[0044] Suitable monomers are for example the acrylic acid andmethacrylic acid esters of mono-, di- or higher-functional alcohols. Asexamples there can be named: methyl (meth)acrylate, iso-butyl(meth)acrylate, ethylene glycol di(meth)acrylate, triethylene glycoldi(meth)acrylate (TEGDMA), hexanediol di(meth)acrylate, dodecanedioldi(meth)acrylate and trimethylolpropane tri(meth)acrylate.

[0045] Also advantageously usable is bisphenol-A di(meth)acrylate aswell as the ethoxy- or propoxylated di(meth)acrylates derived therefrom.The monomers described in U.S. Pat. No. 3,066,112 based on bisphenol-Aand glycidyl(meth)acrylate or their derivatives resulting from theaddition of isocyanates are also suitable.

[0046] Particularly suitable are also the diacrylic and dimethacrylicacid esters of bis(hydroxymethyl)-tricyclo[5.2.1.0^(2.6)]-decane namedin DE-C-28 16 823 and the diacrylic and dimethacrylic acid esters of thecompounds of bis(hydroxymethyl)-tricyclo[5.2.1.0^(2.6)]-decane extendedby 1 to 3 ethylene oxide and/or propylene oxide units.

[0047] Urethane(meth)acrylates, such as7,7,9-trimethyl-4,13-dioxo-5,12-diazahexadecane-1,16-dioxy-dimethacrylate(UDMA), can also be a constituent of the component (C2).

[0048] Fillers according to component (C3) can be inorganic fillers, forexample quartz, ground glasses, non-water-soluble fluorides such asCaF₂, silica gels such as silicic acid, in particular pyrogenic silicicacid and granulates thereof. Cristobalite, calcium silicate, zirconiumsilicate, zeolites, including the molecular sieves, metal oxide powders,such as aluminium or zinc oxides or their mixed oxides, barium sulphate,yttrium fluoride, calcium carbonate can also be used as fillers.

[0049] Fluoride-releasing fillers, for example complex inorganicfluorides of the general formula A_(n)MF_(m) as described in DE-A-44 45266, can be used or added. A represents a mono- or polyvalent cation, Ma metal of the IIIrd, IVth, Vth main or sub-group, n an integer from 1to 3 and m an integer from 4 to 6.

[0050] Organic fillers can also be a constituent of the component (C3).As examples there can be named customary methyl methacrylate-based beadpolymers and copolymers, which can be obtained for example from Röhmunder the name “Plexidon” or “Plex”.

[0051] For better incorporation into the polymer matrix, it can beadvantageous to hydrophobize the named fillers and, if present,X-ray-opaque additives. The quantity of silane used is usually 0.5 to 10wt.-% relative to inorganic fillers, preferably 1 to 6 wt.-%, quiteparticularly preferably 2 to 5 wt.-% relative to inorganic fillers.Customary hydrophobing agents are silanes, for exampletrimethoxymethacryloxypropyl silane. The maximum average particle sizeof the inorganic fillers is preferably 15 μm, in particular 8 μm.Fillers with an average particle size of <3 μm are quite particularlypreferably used.

[0052] By initiators according to component (C4) are meant initiatorsystems which effect the radical polymerization of the monomers, forexample photoinitiators and/or so-called redox-initiator systems and/orthermal initiators.

[0053] Suitable as photoinitiators are for example α-diketones such ascamphorquinone, in combination with secondary and tertiary amines, ormono- and bisacylphosphinic oxides such as2,4,6-trimethylbenzoyldiphenyl-phosphinic oxide andbis-(2,6-dichlorobenzoyl)-4-n-propylphenyl-phosphinic oxide. However,other compounds of this type as described in European patentpublications EP-A-0 073 413, EP-A-0 007 508, EP-A-0 047 902, EP-A-0 057474 and EP-A-0 184 095 are also suitable.

[0054] Organic peroxide compounds together with so-called activators aresuitable as redox initiator systems. In particular, compounds such aslauroyl peroxide, benzoyl peroxide and p-chlorobenzoyl peroxide andp-methylbenzoyl peroxide can be considered as organic peroxidecompounds.

[0055] Suitable as activators are, for example, tertiary aromaticamines, such as the N,N-bis-(hydroxyalkyl)-3,5-xylidines known from U.S.Pat. No. 3,541,068 as well asN,N-bis-(hydroxyalkyl)-3,5-di-t-butylanilines known from DE-A-26 58 530,in particular N,N-bis-(β-oxybutyl)-3,5-di-t-butylaniline as well asN,N-bis-(hydroxyalkyl)-3,4,5-trimethylaniline.

[0056] Well-suited activators are also the barbituric acids andbarbituric acid derivatives described in DE-B-14 95 520 as well as themalonyl sulfamides described in EP-A-0 059 451. Preferred malonylsulfamides are 2,6-dimethyl-4-isobutylmalonyl sulfamide,2,6-diisobutyl-4-propylmalonyl sulfamide, 2,6-dibutyl4-propylmalonylsulfamide, 2,6-dimethyl4-ethylmalonyl sulfamide and2,6-dioctyl4-isobutyl malonyl sulfamide.

[0057] For further acceleration, the polymerization is in this casepreferably carried out in the presence of heavy-metal compounds andionogenic halogen or pseudohalogen. Copper is particularly suitable asheavy metal, chloride ion as halide. The heavy metal is suitably used inthe form of soluble organic compounds. Likewise, the halide andpseudohalide ions are suitably used in the form of soluble salts, asexamples there can be named the soluble amine hydrochlorides as well asquarternary ammonium chloride compounds.

[0058] If the dental compounds according to the invention contain aredox initiator system comprising organic peroxide and activator,peroxide and activator are preferably present in parts of the dentalcompound according to the invention physically separated from oneanother and are homogeneously mixed together only immediately beforeuse. If organic peroxide, copper compound, halide and malonyl sulfamideand/or barbituric acid are present next to each other, it isparticularly useful for the organic peroxide, malonyl sulfamide and/orbarbituric acid and the combination of copper compound/halide to bepresent in three constituents physically separated from one another. Forexample, the combination of copper compound/halide, polymerizablemonomers and fillers can be kneaded to a paste and the other componentskneaded to two separate pastes in the above-described manner each with asmall quantity of fillers or in particular thixotropic auxiliaries, suchas silanized silicic acid, and a plasticizer, for example phthalate. Onthe other hand, the polymerizable monomers can also be present togetherwith organic peroxide and fillers. Alternatively, a distribution oforganic peroxide, copper compound, halide and malonyl sulfamide and/orbarbituric acid can be realized according to DE-A-199 28 238.

[0059] As representatives of the component (C5), soluble organicpolymers can for example be used to increase the flexibility of thecompounds. Suitable are for example polyvinyl acetate as well ascopolymers based on vinyl chloride/vinyl acetate, vinyl chloride/vinylisobutyl ether and vinyl acetate/maleic acid dibutyl ether. Well-suitedas additional plasticizers are for example dibutyl, dioctyl and dinonylphthalates or adipates as well as higher-molecular polyphthalic acid andadipic acid esters. There can also be used as thixotropic auxiliaries,in addition to pyrogenic silicic acids, modified layered silicates(bentonites) or organic modifiers, for example on the basis ofhydrogenated castor oils.

[0060] Furthermore, retardants as described in EP-A-0 374 824 ascomponent (d) can also be contained as additives in the formulations.

[0061] The components according to the invention can be distributed forexample over two pastes as follows:

[0062] Paste 1: Parts of C3, parts of C4, C5

[0063] Paste 2: C1, C2, parts of C3, parts of C4.

[0064] Dental materials which contain the urethane prepolymers accordingto the invention can be used for example as filling materials, cements,temporary crown and bridge materials, facing plastics, prosthesismaterials, orthodontic materials, plastics for fissure sealing,modelling plastics or model plastics.

[0065] The urethane prepolymers according to the invention andformulations prepared therefrom are also suitable for the gluing andcoating of substrates. As examples can be named the coating of wood,metal, glass or plastic. Furthermore, the urethane prepolymers accordingto the invention and formulations prepared therefrom are also suitablefor the preparation of moulded bodies.

[0066] Preferably, compounds containing the urethane prepolymersaccording to the invention are formulated as two-component mixtures,these preferably being packed into a cartouche system and the compoundsapplied via a static or dynamic mixing set, homogeneously mixed andcured.

[0067] In the following, the invention is explained in more detail bymeans of examples, the latter not to be seen as limiting the inventionin any way.

EXAMPLES Preparation Example 1 Urethane Acrylate

[0068] 212 g (approx. 0.2 mol) Tego-Diol BD-1000, 70 g ethyl acetate and0.1 g dibutyltin dilaurate are introduced into a 2 l 3-neck flaskequipped with thermometer, reflux cooler, mechanical stirrer and dryingtube, and 126 g (0.6 mol) trimethyl-hexamethylene diisocyanate added inmeasured doses, accompanied by cooling, over a period of 30 minutes. Thereaction mixture is stirred for 20 hours at room temperature until theisocyanate content has fallen to 7.7%. 91 g hydroxyethylacrylate isadded accompanied by cooling. After 72 hours at room temperature, anisocyanate value of 0 is recorded, at which the reaction is ended. Theethyl acetate can be distilled off in fine vacuum.

Preparation Example 2 Urethane Methacrylate

[0069] 212 g (approx. 0.2 mol) Tego-Diol BD-1000, 140 g acetone and 0.1g dibutyltin dilaurate are introduced first into a 2 l 3-neck flaskequipped with thermometer, reflux cooler, mechanical stirrer and dryingtube, and 84 g (0.4 mol) trimethyl-hexamethylene diisocyanate added inmeasured does, accompanied by cooling, over a period of 30 minutes. Thereaction mixture is stirred for 20 hours at room temperature until theisocyanate content has fallen to 3.7%. 53 g hydroxyethyl methacrylate isadded, accompanied by cooling. After 72 hours at room temperature, anisocyanate value of 0.1 is recorded, at which the reaction is ended. Theethyl acetate can be distilled off in fine vacuum.

Application Examples

[0070] 10 g catalyst and 100 g base paste each are kneaded from theconstituents listed in Table 1 and Table 2. These are packed into 10:1cartouches from Mixpack, Rotkreuz. To apply them, they are pressedthrough a static mixing device by means of a dispenser and mixed, sothat curing occurs within several minutes. TABLE 1 Catalyst ComponentConstituent Quantity [g] Wt.-% C3 Fluoroaluminosilicate glass 3.4 34powder (φ < 12 μm) C3 Silanized microfine silicic 0.7 7 acid (HDKH 2000,Wacker, Burghausen) C4 1-benzyl-5-phenyl 0.1 1 barbituric acid C43,5,5-trimethylhexanoic 0.06 0.6 acid tertiary butyl ester C52,2-bis-4-(2- 5.74 57.4 hydroxyethoxyphenyl)- propane-bis-acetate

[0071] TABLE 2 Component Quantity [g] Wt.-% Application example 1 Base 1C3 Fluoroaluminosilicate 25 25 glass powder (φ < 12 μm) silanized withmethacryloxypropyl trimethoxy silane C3 Silanized microfine silica 7 7acid (HDKH 2000, Wacker) C4 Bis(1-phenylpentane- 0.00775 0.007751,3-dionato)-copper(II) C4 (β-phenylethyl)-dibutyl- 0.352 0.352ammonium-chloride C1 Urethane acrylate: 13.6 13.6 Preparation example 1C2 2,2-bis-4(acryloxy- 54.04025 54.04025 bisethylene glycol)-phenylpropane Application example 2 Base 2 C3 Fluoroaluminosilicate 2525 glass powder (φ < 12 μm) silanized with methacryloxypropyl trimethoxysilane C3 Silanized microfine silic 7 7 acid (HDKH 2000, Wacker) C4Bis-(1-phenylpentane- 0.00775 0.00775 1,3-dionato)-copper(II) C4(β-phenylethyl)-dibutyl- 0.352 0.352 ammonium-chloride C1 Urethanemethacrylate: 13.6 13.6 Preparation example 2 C2 2,2-bis(4-acryloxy-54.04025 54.04025 bisethylene glycol)- phenylpropane Quantity [g] Wt.-%Comparison example 1 Base 3 Fluoroaluminosilicate 25 25 glass powder (φ< 12 μm) silanized with methacryloxypropyl trimethoxy silane Silanizedmicrofine silic 7 7 acid (HDKH 2000, Wacker) Bis(1-phenylpentane-0.00775 0.00775 1,3-dionato)-copper(II) (β-phenylethyl)-dibutyl- 0.3520.352 ammonium-chloride Polyesterurethane- 13.6 13.6 acrylate 98-446(Rahn) 2,2-bis-4(acryloxy- 54.04025 54.04025 bisethylene glycol)-phenylpropane Comparison example 2 Base 4 Fluoroaluminosilicate 25 25glass powder (φ < 12 μm) silanized with methacryloxypropyl trimethoxysilane Silanized microfine silic 7 7 acid (HDKH 2000, Wacker)Bis-(1-phenylpentane- 0.00775 0.00775 1,3-dionato)-copper(II)(β-phenylethyl)-dibutyl- 0.352 0.352 ammonium-chloridePolyesterurethane- 13.6 13.6 acrylate BR-372 (Bomar) 2,2-bis-4(acryloxy-54.04025 54.04025 bisethylene glycol)- phenylpropane

[0072] The following measurement values were obtained with the curedtestpieces: TABLE 3 Linear Polyurethane swelling, Bending on Impact(meth) 7d in 36° C. E-modulus fracture strength Base acrylate H₂O [%][Mpa] [mm] [kJ/m²] 1 Urethane 0.2 1450 1.7 9.41 acrylate: Preparationexample 1 2 Urethane 0.25 1200 1.3 9.97 methacrylate: Preparationexample 2 3 Polyester- 0.35 900 1.4 4.89 urethane- acrylate 98-446(Rahn) 4 Polyether- 0.4 1000 1.2 4.42 urethane- acrylate BR-372 (Bomar)

[0073] The testpieces prepared with the base pastes 3 and 4 notaccording to the invention display an increased swelling, a reducedE-modulus and a much reduced impact strength compared with thetestpieces made from pastes according to the invention (base 1 and 2).

1. Urethane prepolymers, obtainable by reaction of: (A) 15 to 85 wt.-%of one or more α,ω-terminated poly(meth)acrylate diols, (B) 0 to 30wt.-% of one or more radically curable, polyhydroxy-functionalcompounds, (C) 14 to 60 wt.-% of one or more polyisocyanates, (D) 1 to40 wt.-% of a monofunctional compound, reactive vis-à-vis isocyanategroups, which also contains one or more radically curable groupings. 2.Urethane prepolymers according to claim 1, the representatives of thecomponent (B) displaying OH numbers from 40 to 700 mg KOH/g, inparticular polyhydroxy-group-containing polyester(meth)acrylateprepolymers, polyhydroxy-group-containing polyepoxy(meth)acrylateprepolymers, polyhydroxy-group-containing polyurethane(meth)acrylateprepolymers.
 3. Urethane prepolymers according to one of claims 1 or 2,the representatives of the component (C) being of an aliphatic,cycloaliphatic and/or aromatic nature and displaying at least two freeisocyanate groups.
 4. Urethane prepolymers according to one of claims 1to 3, the representatives of the component (C) being diisocyanatesX(NCO)₂, X representing an aliphatic hydrocarbon radical with 2 to 12 Catoms, a cycloaliphatic hydrocarbon radical with 5 to 18 C atoms, anaromatic hydrocarbon radical with 6 to 16 C atoms and/or an araliphatichydrocarbon radical with 7 to 15 C atoms.
 5. Urethane prepolymersaccording to one of claims 1 to 4, the representatives of the component(D) having a hydroxy group and, as radically curable groupings,(meth)acrylate groups.
 6. Use of the urethane prepolymers according toone of claims 1 to 5 for the preparation of dental compounds as well asfor the gluing, coating or pouring of substrates, in particular for thepreparation of filling materials, stump build-up materials, fixingcements, temporary crown and bridge materials, dental materials, modelmaterials, inlays, onlays, facing shells, crowns and bridges. 7.Compositions, containing: (C1) 1 to 70 wt.-% of at least one urethaneprepolymer according to one of claims 1 to 5, (C2) 8.9 to 70 wt.-% ofone or more radically polymerizable monomers, (C3) 10 to 90 wt.-%fillers, (C4) 0.1 to 5 wt.-% initiators and optionally activators, (C5)0 to 30 wt.-% additives, optionally pigments, thixotropic auxiliaries,plasticizers.
 8. Compositions according to claim 7, mono-, di- and/orhigher-functional acrylic acid and/or methacrylic acid esters being usedas component (C2), which can contain both monomeric and higher-molecularoligomeric or polymeric acrylates and are used alone or in a mixture. 9.Use of the compositions according to one of claims 7 to 8 in the dentalfield, in particular as filling material, stump build-up material,fixing cement, temporary crown and bridge material, dental material,model material, inlay, onlay, facing shell, crowns and bridges.
 10. Kitfor the preparation of dental materials optionally containing anapplicator for the dispensing of dental materials, optionally a staticmixing set, at least one cartouche with at least two chambers which arefilled with a composition according to one of claims 7 to
 8. 11. Curedcomposition according to one of claims 7 to
 8. 12. Applicator,containing at least one cartouche, containing a composition according toone of claims 7 to 8.